1. Field of the Invention
The present invention relates to methods for fabricating a semiconductor device, and more particularly, to a method for forming a silicide film in a semiconductor device, which can prevent a silicide reaction from occurring in a region where the silicide is not formed.
2. Discussion of the Related Art
Presently, as degrees of semiconductor device concentration increases, a sheet resistance of wiring increases due to decrease of width of the wiring. The increase of the sheet resistance of the wiring delays a signal transmission time period of a device in an integrated circuit. For preventing this, a refractory silicide which has low resistivity, and is stable at a high temperature is added to connections, not only to a gate electrode, but also to source/drain, to drop the sheet resistance and contact resistance of the wiring. Such a silicide includes a rare earth metal reactive with silicon. Such silicides include tungsten silicide (WSi2), titanium silicide (TiSi2), cobalt silicide (CoSi2), and so on.
FIG. 1 illustrates a flow chart showing the steps of a related art method for forming a silicide film in a semiconductor device, and FIGS. 2A˜2E illustrate sections showing the steps of a related art method for forming a silicide film in a semiconductor device, referring to which the related art method for forming a silicide film in a semiconductor device will be described.
Referring to FIG. 2A, after a semiconductor device fabricating process is performed on a silicon substrate 10 as a semiconductor substrate, a silicon oxide SiO2 film, or a silicon nitride Si3N4 film is formed as a silicide suppression film 12 on the silicon substrate 10 for defining a region for forming a silicide film thereon. (S10)
A photo process is performed, to form a photoresist pattern 14 on the silicide suppression film 12.
Referring to FIG. 2B, the silicide suppression film exposed from the photoresist pattern 14 is subjected to dry or wet patterning, to form a silicide suppression film pattern 12a. The silicide suppression film pattern 12a serves to suppress a silicide reaction from occurring between the silicon substrate and a metal in a silicide forming step later. (S20)
Referring to FIG. 2C, a rare earth metal film 16 of, such as tungsten W, titanium Ti, cobalt Co, or so on is deposited on surfaces of the silicide suppression pattern 12a, and the silicon substrate 10, for forming a silicide. (S30)
Then, referring to FIG. 2D, a heat treatment process is performed for making a silicide reaction between the metal film 16 and the silicon substrate 10, so that a silicide film 18 is formed on a silicon substrate 10 region exposed from the silicide suppression pattern 12a, excluding the silicide suppression pattern 12a. (S40) That is, since the silicon oxide film, or the silicon nitride film, or the like of the silicide suppression film pattern 12a does not make reaction with the metal film 16 well, though the silicon oxide film, or the silicon nitride film is not turned into a silicide film, since the silicon of the silicon substrate 10 makes reaction with the metal film 16 well, the silicon is turned into a silicide film. The silicide film 18 may be formed of, for example, tungsten silicide WSi2, titanium silicide TiSi2, cobalt silicide CoSi2, and so on.
Then, referring to FIG. 2E, upon removal of the metal film 16 which is not turned into a silicide film, excluding the silicide film 18, the silicide film 18 and the silicide suppression film pattern 12a are remained on the silicon film 10 (S50). Thereafter, the silicide suppression film pattern 12a is removed as required.
Therefore, by forming the silicide film on a region of the semiconductor device by the related art method for forming a silicide film, the sheet resistance or the contact resistance of a region having the silicide film formed thereon can be dropped.
However, with regard to the silicide suppression film pattern 12a on only an opened selected region of which the silicide film is formed by the related art method for forming a silicide, the silicide suppression film pattern 12a is subjected to dry or wet patterning.
However, it is difficult to etch the silicide suppression film pattern 12a into a desired pattern shape accurately by the isotropic etching of the wet etching. Moreover, though the dry etching, mostly by using plasma, enables accurate etching of the silicide suppression film pattern 12a because a plasma generating chamber and an etching chamber are within the same chamber, the photoresist pattern deforms because the plasma generation and the etching occur within one chamber, to require an oxygen ashing additionally for removing a deformed photoresist pattern, which is cumbersome.